You would hate to imagine where the San Francisco 49ers would be at with their wide receivers if they had not swung a trade for Anquan Boldin.

With top receiver Michael Crabtree sidelined until the end of November (at the very earliest) with a torn Achilles tendon the 49ers are sorting their way through options. The plan, of course, was for Crabtree to operate opposite Boldin much of the time. Crabtree really came into his own last season and was outstanding in the club’s playoff push.

Now, Boldin will have to be more of a primary target for quarterback Colin Kaepernick as the staff works its way through a lot of secondary options.

“Very impressed,” 49ers coach Jim Harbaugh said Tuesday after watching Boldin participate in the team’s OTA. “Today, you got a good look at what he’s been doing. Really picked up the system fast and making plays. Big catches in tight areas. You saw what we’ve been seeing for a couple of weeks now, very good.”

As the spring and summer unfolds, it’s possible Boldin becomes a leader for the young players at the bottom of the depth chart.

“That could be something that develops,” Harbaugh said. “Right now, Anquan is not a talkative guy. He’s not a small-talk guy. He’s just very serious about competing, and very serious about football and winning. I think it’ll speak volumes if the young guys observe that.”

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Brad Biggs covers the Bears for the Chicago Tribune